The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-052324 filed on Feb. 27, 2001 the entire contents thereof are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a GPS antenna for a two-wheeled motor vehicle and more particularly to a GPS antenna for a two-wheeled motor vehicle which can be mounted without impairing the appearance of the two-wheeled motor vehicle.
2. Description of Background Art
A GPS antenna for a four-wheeled motor vehicle, such as a private vehicle, is disclosed in Japanese Patent Laid-open No. Hei 4-326202. As set forth in this patent, a plane antenna, also referred to as a patch antenna, is provided which is square in shape, 20 to 60 mm long by 20 to 60 mm wide, or which is in the shape of a disc having a diameter of 20 to 60 mm. In such a plane antenna, a large number of antenna elements can be integrated and therefore there can be attained an extremely high directivity in the vertical direction. In addition, the adoption of a diversity configuration provides a good condition for reception.
In a navigation system which utilizes GPS, it is known that when utilized a radio wave transmitted from a satellite with an elevation angle close to the horizon, the system is strongly influenced by a multi-path and an ionospheric delay or the like to deteriorate the accuracy. On the other hand, the abobe-described plane antenna is high in its directivity in the vertical direction and is low in its sensitivity in the horizontal direction, so it is difficult to be influenced by a multi-path and an ionospheric delay.
In a four-wheeled motor vehicle there is a sufficient plane portion on a bonnet, a roof, or a trunk, so a plane antenna can be installed in that plane portion. On the other hand, there are few plane portions included in the surface of a two-wheeled motor vehicle and therefore it is difficult to ensure sufficient space for the installation of a plane antenna.
Accordingly, if a plane antenna is adopted, it is necessary to not only alter the existing shape and design but also to ensure a special space for the plane antenna. Thus, a technical problem exist in that the shape and design of the vehicle body requires a change, impairing the appearance of the vehicle body.
Further, if a plane antenna is adopted for a GPS of a moving body which undergoes a great change in posture during travel, such as a two-wheeled motor vehicle, then in a tilted state of the vehicle body, a strong directivity of the plane antenna acts on a radio wave emitted from a satellite with a low elevation angle, with consequent deterioration of the accuracy.
It is an object of the present invention to solve the above-mentioned problems involved in the prior art and provide a GPS antenna unit for a two-wheeled motor vehicle which can be installed in the two-wheeled motor vehicle without impairing the appearance of the vehicle.
According to the present invention, for achieving the above-mentioned object, there is provided a GPS antenna unit for a two-wheeled motor vehicle, mounted to the two-wheeled motor vehicle to receive a radio wave from a GPS satellite, including a helical antenna extending to the exterior from a unit case and a controller accommodated within the unit case to process the radio wave received by the helical antenna.
According to the above feature, it is possible to diminish the projection area of the GPS antenna and therefore the GPS antenna can be mounted to even to a two-wheeled motor vehicle having few planar portions which face the zenith, without impairing the appearance and aerodynamic characteristics of the vehicle.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.